The percentages indicate how much of the ball's surface area is not visible. The thicker your lie, the worse distance you'll get from it.
As a rule of thumb, in the rough, 20-25% lies are about 1/2 club up. 30-40% lies are about a club or a little more. 40-50% lies are 2-3 clubs. Different types of shots are affected in different ways by these various lies, so there's really no substitution for practice here.